Pathogenesis of Nerve Injury: Role of Tissue Inhibitor of Metalloproteinases-1

Extremity (e.g., leg) trauma accounts for the majority of combat wounds and causes peripheral nerve injury. Despite the high regenerative capacity of the peripheral nervous system (PNS), patients develop severe sensorimotor abnormalities and neuropathic pain (NP) sustaining for years after injury. In the framework of this VA Merit program (since 2005), we have pioneered research on tissue inhibitor of metalloproteinases (TIMP)- 1 in the PNS injury-related NP as an endogenous inhibitor of the matrix metalloproteinases (MMPs) and have demonstrated robust pro-regenerative and analgesic activity of both synthetic MMP inhibitors (MMPi) and TIMPs in the PNS. Given the emerging evidence for sexual dimorphism in mechanisms of PNS injury and NP, since 2020, we have focused the present study of TIMP-1 as an X-chromosome-encoded, top-induced early- response gene in the damaged PNS. Using ground-breaking concepts and innovative tools (e.g., BioID/TIMP constructs, TIMP1-enriched EVs, TIMP1-activating CRISPR-CAS9 system, RNAseq, LC-MS mass spectrometry, bioinformatics), we provide the first evidence of TIMP-1’s novel and/or sex-dependent myelin membrane MMTIMP-1 isoform and implicate TIMP-1 in sex-dependent establishment of extracellular vesicle (EV) transport by association with chaperone, cytoskeletal and scaffolding proteins. We hypothesize that in addition to the classical (secreted) isoform of TIMP-1 that inhibits MMPs and binds receptors, MMTIMP-1 contributes to the sex-specific EV transport to DRG neuronal soma. We aim to establish Schwann cell (Aim 1) and sensory neuronal (Aim 2) functions of the classical (secreted), MMTIMP-1 and intracellular TIMP-1 isoforms in exosome formation and sex-specific neurotrophic, neuroprotective and anti-apoptotic activities. We are eager to continue this trailblazing work, aiming to ultimately develop a novel non-addictive, neuroprotective, regenerative and analgesic TIMP1-containing EV and/or neuron-targeted TIMP-1 gene therapy (Aim 3).